1. Field of Invention
The present invention relates to a liquid crystal display and, more particularly, to an LCD to which a color filter on array structure is applied and a method of manufacturing the LCD.
2. Description of the Prior Art
A liquid crystal display (LCD) comprises a lower substrate with thin film transistors (TFTs), pixel electrodes and the like formed thereon, an upper substrate with a common electrode and the like formed thereon, and a liquid crystal layer formed between the lower and upper substrates. When a voltage is applied to pixel and common electrodes of such an LCD, an electric field is generated in the liquid crystal layer due to the potential difference applied between the two electrodes. The alignment of liquid crystal molecules are changed in accordance with the intensity of the electric field. A change in the alignment of the liquid crystal molecules causes the polarization of the light passing through the liquid crystal layer to be changed, which leads to a change in the light transmittance due to a polarizer provided on the outer surface of the substrate.
In a conventional LCD, the lower substrate is formed with TFTs, pixel electrodes and the like, and the upper substrate is formed with color filters, a black matrix, a common electrode and the like. However, since the color filters and TFTs should be formed on different substrates, the manufacturing process of such an LCD is complicated. It has been suggested that a structure known as the COA structure be used which provides the color filter on the same substrate with the TFT array.
In an LCD having a COA structure, the color filters may be formed on top of an organic insulation film formed on the lower substrate Alternatively, the color filters may be formed singly in place of the organic insulation film. Where color filters are singly formed, the color filters should be formed to be about two or more times thicker than the usual photoresist. Since the dielectric constant of the color filters is similar to that of the organic insulation film, the color filters are formed with a thickness of 3.0 μm or so, the same as the organic insulation film would be. Further, contrary to the conventional LCD in which color filters are formed on an upper substrate, when the color filters are formed on the lower substrate, the data lines serve as the black matrix and the respective red, green and blue color filters should be formed to overlap the data lines whose width is designed to be 10 to 15 μm or so, as for a conventional LCD.
Such a COA structure has been applied to S-PVA (Super-Patterned Vertical Alignment) display apparatus. In the S-PVA, each pixel is configured to have two sub-pixels and differential voltages are applied to the respective sub-pixels so as to improve the side gray level rounding or reversal, thereby enhancing side visibility. In the LCD having the S-PVA structure, two transistors and two pixel electrodes are provided in a pixel region for expressing one color. The LCD having the S-PVA structure naturally expresses gray levels using a method of applying different peak voltages to the respective pixel electrodes in order to alleviate the side visibility distortion phenomenon.
In an LCD using COA and S-PVA structures, a color filter is not formed on top of the storage electrode of the lower substrate. Accordingly, only a protection film and a gate insulation film exist in such a region of the storage electrode with which to form the dielectric of the storage capacitor between the pixel and storage electrodes.
The color filters for the LCD using COA and S-PVA structures, are formed to have a thickness of 3 μm or more. However, since the photoresist for patterning pixel electrodes is formed to be thinner than the color filters, the thickness of the photoresist changes rapidly at the boundary between a region in which the color filters are formed and a region in which the color filters are not formed. The photoresist formed in such a step portion may not properly be exposed during the light exposing process and the photoresist may not be completely removed in the photoresist developing process. When the photoresist remains in the step portion of the color filters, the conductive layer for forming the pixel electrodes remains in the subsequent wet etching process of the pixel electrodes. Therefore, there is a problem in that two sub-pixels are shorted to each other due to the conductive layer remaining in the step portion between a region in which color filters are formed and a region in which the color filters are not formed.